the development of a personal dosimeter for vinyl chloride
TRANSCRIPT
Louisiana State UniversityLSU Digital Commons
LSU Historical Dissertations and Theses Graduate School
1976
The Development of a Personal Dosimeter forVinyl Chloride Utilizing the Permeation Approach.Leonard Hoyt NelmsLouisiana State University and Agricultural & Mechanical College
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Xerox University Microfilms300 North Zeeb RoadAnn Arbor, Michigan 48106
76- 25,277NELMS, Leonard Hoyt, 1946- THE DEVELOPMENT OF A PERSONAL DOSIMETER FOR VINYL CHLORIDE UTILIZING THE PERMEATION APPROACH.
The Louisiana State University and Agricultural and Mechanical College, Ph.D., 1976 Chemistry, analytical
Xerox University Microfilms f Ann Arbor, Michigan 48106
THE DEVELOPMENT OF A PERSONAL DOSIMETER FOR VINYL CHLORIDE UTILIZING
THE PERMEATION APPROACH
A Dissertation
Submitted to the Graduate Faculty of the Louisiana State University and
Agricultural and Mechanical College in partial fulfillment of the
requirements for the degree of Doctor of Philosophy
in
The Department of Chemistry
byLeonard Hoyt Nelms
S. S., The University of Georgia, I968 M. A., The University of North Carolina, I972
May, 1976
To my wife and daughter, in recognition of their patience and understanding during the course of this work.
11
ACKNOWLEDGEMENTS
The author wishes to express his sincere appreciation to
Dr. Philip W. West for his guidance and counsel over the course
of this research. His influence will be remembered and appreciated
by the author for many years to come.The author would also like to express his gratitude to all
of the other members of Dr. West's research group, past and present
who have participated in the many valuable discussions of this research project, and especially to Dr. Kenneth D. Reiszner for his
assistance in the development of this device.
The author is also Indebted to Mr. G. C. Gaeke for his valuable
discussions and assistance over the course of this work, and to Ethyl Corporation for their interest in and support of this work.
The author would like to thank the National Science Foundation
and the Occupational Safety and Health Administration for their
financial support of this research.
ill
TABLE OF CONTENTS
PAGE
DEDICATION.......................................... 11
ACKNOWLEDGEMENTS ..................................... 111
LIST OF TABLES ............................... viiLIST OF FIGURES ...................................... viii
ABSTRACT ............................................ **
CHAPTERI. INTRODUCTION ................................ 1
A. Sources of Vinyl Chloride ................. ^
B. Importance and Health Effects .............. ^C. Present Methods for Determination of Vinyl
Chloride in the Workplace and in Ambient
Air ..................................... UD. Development of the Present Method.......... 15
II. EXPERIMENTAL................................ 19
A. Apparatus for Exposure Studies ............ 19
1. Basic Design of Equipment for Vinyl
Chloride Exposure ..................... 192. Design and Preparation of Permeation
Tubes ............................... 193. Calibration and Use of Permeation
Tubes ............... ................
Preparation of Standard Vinyl
Chloride Atmospheres .................. ^
iv
CHAPTER PAGE5. Flowmeters ........................ 27
6. Permeation Device for PreliminaryStudies ...................... 29
7* Additional Constant Temperature Baths .... 298. Standards for Instrumental Calibration..,. 299. Humidity Studies ............. 33
10. Interference Studies .................. 3311. Design of the Personal Monitoring Device.. 55
B. Instrumentation........................... 36
1. Gas Chromatograph ..................... 36
2. Column............................... 39
3. Recorder........................... 394. Apparatus for Thermal Desorption....... 39
C. Reagents and Materials ....................
1. Vinyl Chloride ..................... 41
2. Activated Charcoal .................... 41
3. Chromosorb 102.............. 41D. Analytical Procedure ...................... 41
III. RESULTS AND DISCUSSION ....................... 43A. Theory of Permeation in Polymers ........... 43
B. Determination of the Permeation Constant 46C. Experimental Conditions for the Determination
of Vinyl Chloride ........................ 46
D. Temperature Effect ................... 47
v
CHAPTER PAGEE. Response of the System to Various
Vinyl Chloride Levels ...... ............. 48F. Response Time .......................... 54
G. Humidity Effect ......................... 5H. Interference Studies ................. 56
I. Field Evaluation............. 56
IV. CONCLUSIONS .................................. 62BIBLIOGRAPHY....................................... 65
VITA............................................... 73
vl
LIST OF TABLESTABLE PAGEI. CALIBRATION DATA FOR A TYPICAL VINYL
CHLORIDE PERMEATION TUBE................... 2k
II. EFFECT OF GEOMETRY ON VINYL CHLORIDE
DESORPTION ............................... 53
III. EFFECT OF COMMON INTERFERENTS ON VINYL
CHLORIDE DETERMINATION..................... 57
IV. COMPARISON OF RESULTS OBTAINED WITH THE
PERMEATION METHOD TO THOSE USING PUMPS ...... 59
vii
LIST OF FIGURES
FIGURE PAGE1. THE VINYL CHLORIDE PERMEATION TUBE .............. 202. PERMEATION TUBE FOR LOW-LEVEL WORK.............. 22
5. APPARATUS FOR PREPARATION OF VINYLCHLORIDE-AIR MIXTURES ........................ 26
k. MIXING CHAMBER FOR USE WITH VINYL
CHLORIDE PERMEATION TUBES ..................... 28
5. PERMEATION DEVICE USED FOR PRELIMINARY STUDIES 50
6. EQUIPMENT FOR PREPARATION OF VINYL
CHLORIDE STANDARDS ........................... 52
7. DIFFUSION TUBE FOR VOIATILE LIQUIDS ............. $k
8. DESIGN OF A PERSONAL MONITORING DEVICE
FOR VINYL CHLORIDE........................... 579. MODIFIED VARIAN 1200 GAS CHROMATOGRAPH
FOR VINYL CHLORIDE DETERMINATIONS ............. 5810. APPARATUS FOR THERMAL DESORPTION OF
VINYL CHLORIDE..............................
11. EFFECT OF TEMPERATURE ON PERMEATION
OF VINYL CHLORIDE............................ k9
12. RESPONSE OF THE PERMEATION DEVICE TO
VARIOUS LEVELS OF VINYL CHLORIDE.............. 5*15. RESPONSE TIME OF THE PERMEATION DEVICE
TO VINYL CHLORIDE............................ 55
viii
ABSTRACT
The necessity for the development of a simple personal monitoring device for vinyl chloride has received broad coverage in recent years in both the scientific and public press. The fact that at least twenty-eight workers have died as a direct consequence of exposure to vinyl chloride vapors has resulted in a drastic
reduction In the allowed levels of the monomer in the industrial environment. The maximum permissible levels of exposure under
current Federal regulations are one part-per-million time-weighted
average for an eight hour period, with a maximum exposure of five
parts-per-million for no more than fifteen minutes. The procedures
coranonly used for vinyl chloride determination are sampling by means
of battery-powered pumps using activated charcoal as a trap, followed by a gas chromatographic finish, or automatic area monitoring..
The battery-powered pump method has the disadvantage of being both
bulky and noisy, although it does monitor the actual breathing
zone of the worker. Automatic area monitoring requires the use of elaborate and expensive equipment, but does not determine the vinyl chloride concentration to tfiich the worker is actually exposed.
Therefore, a definite need exists for a personal monitoring device
that is both easy to use, and effective.A new device is being proposed which is small, lightweight,
and requires no external power supply. It is capable of providing
integrated values for vinyl chloride exposure over periods ranging
from an hour to several days. The device Is inexpensive, reusable,
ix
and free from any significant Interferences. The finish used for the analytical determination are Identical to those currently In
use, hence no new Instrumentation Is required.The method utilizes the permeation method for sampling the
atmosphere around the worker. A small device, 4.2 by 4.8 centimeters,
is attached to the pocket or lapel of the worker's clothing. The
device has a permeable membrane covering a cavity filled with activated charcoal. As the vinyl chloride permeates the membrane
at a rate proportional to the atmospheric concentration, it is
adsorbed by the charcoal. The average exposure may then be determined
by the usual gas chromatographic methods. A detection limit of one
part-per-bllllon has been observed when thermal desorption of the
vinyl chloride is utilized for the determination. For the more
commonly used procedure, extraction of the organic material by carbon disulfide, a detection limit of less than 50 parts-per-billion Is
projected.
x
CHAPTER I
INTRODUCTION
tfe are living in the most technologically advanced age known
to man. It is this technology that has produced the advances that
allowed us to witness the first footsteps on the hostile and
alien surface of the moon. It is this technology that has produced marvels such as television, automobiles, and airplanes which have forever altered the course of human development. It is
this technology that has brought us "miracle11 drugs that allow us
to live longer, healthier lives; "miracle" fibers that give us
better protection against the elements; and "miracle" fertilizers that allow our world to feed its ever growing population.
These technological advances have developed as a result of the Industrial Revolution which began nearly two centuries ago and
continues to this day.
Not all of the products of the Age of Technology in which
we live have been beneficial to mankind. Our technology has
produced the many weapons of war which are capable of awesome
destrucution of lives and property. It has produced the afore
mentioned automobile, which spews forth a variety of noxious and
hazardous chemicals, while killing or maiming thousands of persons
each year on our highways. It has produced huge factories which
pour tons of hazardous materials into our air and water each year.
It is within some of these factories that one of the most harmful
1
2
aspects of our technological age occurs, the daily exposure of
thousands of workers to hazardous materials, the health effects of which are not known. One of the most recently discovered dangers to the health of these workers is the constant exposure
to vinyl chloride that occurs in the manufacture of the vinyl plastics.
A. SOURCES OF VINYL CHLORIDEVinyl chloride is not a naturally occurlng compound, but
was first synthesized in 1835* For the next century, there was
little further interest in the substance. At the outbreak of World
War II, when Japanese advances In the Far East cut off our supply
of natural rubber, a frantic effort was made to find synthetic
substitutes. One of the families of synthetic rubbers discovered
was the vinyl plastics, formed by the reaction of vinyl chloride
with itself or with various other compounds. Today the bulk
of the vinyl chloride produced in this country is utilized in the
production of polyvinyl chloride polymers. It is also used as
a precursor in the synthesis of various organic compounds, particularly the sulfa drugs, as a refrigerant, and as a propellant
for aerosol sprays.
The first step in the production of vinyl plastics is the synthesis of vinyl chloride. The most coranonly used routes are
the addition of hydrogen chloride to acetylene, and the dehydrohalo-
genation of 1,2-dichloroethane. The vinyl chloride so produced
3
Is a colorless gas, with a boiling point of -I3 .9 degrees Centl-. grade and a faint sweetish odor, not unlike other chlorinated hydrocarbons. The total capacity for vinyl chloride production In the United States in 1970 was 2,h million tons, mostly from
facilities In Louisiana and Texas (1). The major sources of
atmospheric vinyl chloride In these plants is leakage from reaction
vessels and spillage during handling operations.
Over 99 percent of the vinyl chloride produced is utilized
in the manufacture of polyvinyl plastics. Some of the resins
are manufactured at the site of production of the monomer, but
much of the monomer is shipped to various other manufacturers for
the production of their resins. The resinB produced by polymer
manufacturers are often sold in bulk solid form to hundreds of
plastic producers who in turn extrude, mold, press or otherwise reform the material into the final form for sale to users. These
many manufacturers involved in the production of polymeric products
encounter a significant new source of exposure to vinyl chloride.
Upon polymerization, a sometimes sizeable amount of unreacted monomer may be either entrapped or dissolved within the solid
polymer (2). The entrapped monomer then diffuses through the
polymer to the surface where it is released into the atmosphere
by evaporation (3). The largest producer of vinyl chloride in the United States, the B. F. Goodrich Company, has reported (4)
that reductions of vinyl chloride levels in the air are more diffi
cult in its polymer production facilities than in its monomer
1*
production facilities.
The sources mentioned above are of Interest primarily to workers In the plastics industry. They are of concern to the general population only in the event of a major Industrial accident. The sources to which the general population may be exposed are
far less important than these. They include leaching of the
monomer from packaging materials made from vinyl plastics, conta
mination of water supplies by industry, and the release of vinyl
chloride on heating of some vinyl materials. Another hazard,
recently eliminated, was the use of vinyl chloride as a propellant
for aerosol sprays.
B. IMPORTANCE AND HEALTH EFFECTS
Vinyl chloride is not a pollutant to which vast segments of the population are exposed. In fact, exposure is limited
almost entirely to the 1*00 ,000 workers in some 8 ,000 plants pro
ducing either the vinyl chloride monomer and polymer or fabricating
materials from the polymer. The total production of vinyl plastics
is second only to that of polyethylenes. The value of this pro
duction represents nearly one percent of the total Gross National
Product of the United States. Since exposure of the general
population to detectable levels of vinyl chloride is unlikely, the
primary concern in the development of any method for personal
monitoring is its applicability within the industrial environment.
Production of products from vinyl chloride was begun in the
5
19^0's. At that time, vinyl chloride was regarded as having moderate toxicity. The major hazards were considered to be the fire and explosive potentials and the narcotic properties of the
monomer. The explosive limits of vinyl chloride are four to twenty- two percent In air, and the flashpoint Is -7S°C (5). This meant
that exposures of up to four percent or 4j0,000 ppm were permissible from the standpoint of explosiveness. Early studies on the acute toxicity of vinyl chloride showed a narcotic effect on test
animals at concentrations of approximately 8$ for ten minutes (6-9)*
Higher levels usually proved lethal If prolonged for more than a
few minutes. Animals exposed to non-lethal doses were sacrificed
after a recovery period, usually of two weeks duration. No signi
ficant differences were observed between the test animals and
controls.Torkelson, et al. (10), of the Dow Chemical Company, studied
the chronic effects of vinyl chloride exposure In response to
the first real proposal for setting a maximum permissable exposure
limit. They studied the effects of exposure levels ranging from
50 to 5OO ppm on dogs, rats, guinea pigs, and rabbits. They observed very slight changes in liver and/or kidney functions In
rats and rabbits for all exposure levels studied except 50 ppm.
These changes appeared to be reversible, since animals removed from exposure for six to eight weeks appeared to be normal. They
reconmended a standard level of 50 PP*n, but the American Conference
of Governmental Industrial hyglenists accepted the previous
6
reconmendation of 500 ppm in I962.
Researchers at Dow Chemical continued their studies of
workers exposed to vinyl chloride. Kramer, et al. (11) reported
in 1972 their observations of 98 workers exposed routinely to vinyl chloride for periods of up to 25 years. Exposure levels
were found to have averaged I55 ppm in 1950 and only 30 ppm in
I969. Meanwhile, several individuals were found to have received time-weighted-average (TWA) exposures of approximately 300 ppm
over a twenty year period. They found indications of some
possible impairment in liver function, but no clinical evidence of any physiological changes.
In 1970, the Congress of the United States passed the Williams-
Steiger Occupational Safety and Health Act (PL9I-596). This
resulted in the formation of the National Institute for Occupational
Safety and Health, NIOSH, within the Department of Health, Education,
and Welfare; and of the Occupational Safety and Health Administration,
OSHA, within the Department of Labor. NIOSH was charged with conducting research and other studies necessary to formulate re
commendations for Federal regulations to limit occupational hazards. OSHA was made responsible for proposing, adopting, and enforcing
these regulations. At that time, only two deaths due to vinyl
chloride exposure were recorded. Both of these were attributed to
acute overexposure. Hence in 1971» OSHA adopted the previously
defined limits of 5OO ppm TWA allowable exposure. However, these
regulations were to be short-lived.
7
In I97I, Viola, et al. published the first report of possible carcinogenic properties of vinyl chloride (12). Test rats were exposed to three percent V/V vinyl chloride-air mixtures for four hours per day over a period of twelve months. The authors
found that a high percentage of the test animals developed tumors
of the skin, while some also had lung and bone tumors. This study
was largely ignored by industrial hygienists, probably because
the high levels of exposure in this isolated paper were unrealistic
in the industrial environment of that time.A very real concern about the carcinogenicity of vinyl
chloride was awakened in January, 1974. At that time, the B. F. Goodrich Company voluntarily revealed that in 1971 a worker in Its
Louisville, Kentucky plant had died of a rare form of liver cancer.
This was not a cause for alarm until two additional workers in the
same facility died of the same rare disease, identified as angio
sarcoma, in I973. Since the normal rate of occurence for angio
sarcoma is only 0.0014 cases per 100,000 population, the
simultaneous occurrence of three separate cases among such a small
population was immediately recognized as an indication of an
occupational hazard in the plant. Preliminary Investigations
indicated that exposure to vinyl chloride monomer was the probable cause since all three workers had worked in the same polymerization
unit for a long period of time. Since that time at least 26 cases of angiosarcoma among workers in vinyl chloride production facilities
worldwide have been confirmed (13).
8
Immediately following the report by B. F. Goodrich, studies
by Maltonl were published indicating the Induction of liver cancer in laboratory rats at all vinyl chloride levels studied
above 50 PP® In light of these and other findings, OSHAimmediately issued temporary standards of 50 ppm him!mum permissible
exposure in April, 197 > and ordered immediate study of the hazard.In response to the initial reports of cancer induction by
vinyl chloride, the Hew York Academy of Sciences and the American
Cancer Society held a joint meeting on May 10 and 11, 197 . This
gathering was attended by most of those who were doing research
in the field of vinyl chloride hazards. Lange, et al, (16)
reported a high incidence of acroosteolysis of the bones of the
fingers, and frequent severe scaling of the skin associated with
workers involved in the production of polyvinyl chloride plastics.
Miller, et al. (17) reported finding pulmonary function changes,
chronic cough, and up to a 58$ decrease in air flow into the lungs
of those working with vinyl chloride. They were also able to make correlations between the magnitude of the changes and the age
and length of exposure to vinyl chloride of the workers Involved.
Sucln, et al. (18) observed a poisoning effect; Increased dizziness, drowsiness, headaches, and nervousness; a loss of memory; and a fourfold increase in high blood pressure among workers involved
with vinyl chloride production. Berk, et al. (I9) reported a
significant increase in liver injury, predominantly fibrosis,
associated with vinyl chloride exposure. Further, they found that
9
this Injury was not cured by the removal of the worker from continued exposure. Wyatt, et al. (20), and Heath, et.al, (21)
discussed the discovery of the three initial cases of angiosarcoma found at the B. F. Goodrich plant, and the results of screening
tests administered to employees at this and other plants using vinyl chloride or related products. Wyatt revealed the discovery
of two additional cases of angiosarcoma and eleven cases of portal fibrosis at the Louisville location. Nine of the eleven cases
of fibrosis and all of the cases of angiosarcoma were found among
workers in the same production unit that employed the workers
stricken previously. No correlation between blood tests administer
ed to these workers and the amount of vinyl chloride exposure
could be made. Maltoni (22) presented further evidence of the
carcinogenicity of vinyl chloride. Levels greater than 50 ppm were
found to induce the formation of Zymbal gland carcinomas, nephroblastomas, angiosarcomas, angiomas, skin carcinomas, hepatomas,
brain neuroblastomas, lung adenomas, and mammary carcinomas in test animals. Hefner, et al, (23), and Van Duuren (2U) examined
possible metabolic pathways for vinyl chloride in humans. They presented evidence indicating that formation of chloroacetic
acid, chloroethanol, chloroacetaldehyde, and chloroethylene oxide
was the probable means of elimination of vinyl chloride from the
body. They found that elimination was comparatively fast. These
and other reports contained overwhelming evidence that vinyl
chloride was far more hazardous than previously presumed.
10
Acting largely on the evidence presented to the New York
Academy of Sciences, OSHA proposed that standards for allowable
vinyl chloride levels be "none detectable". Industry created anuproar, claiming that these levels were unachievable, and would
close down the entire vinyl Industry. OSHA responded by proposing
a maximum permlssable level of five ppm for no more than fifteen
minutes, and an action level of one-half ppm. Whenever the action level was exceeded, an extensive program for monitoring of
personnel who may be exposed to vinyl chloride was mandated. These regulations were made permanent with the Issuance of the final
standards In October, 197 *
Two other potentially hazardous aspects of vinyl chloride
have been reported recently. Clark and Tinston (25) studied the
sensitization of the heart by a variety of halocarbons, Including vinyl chloride, to adrenaline. It was found that exposure to
vinyl chloride sensitized the heart such that an injection of
adrenaline during exposure produced arrythmias or ventricular
fibrillation. Similar results were found by Aviado and Belej (26)
with vinyl chloride and epinephrine. These studies indicate
that the exposure of workers, particularly those with a tendency
toward heart disease, to high levels of vinyl chloride could under
certain circumstances trigger heart attacks. Malavellle, et al. (27,23) recently reported their observations on the mutagenicity
of vinyl chloride and some of its presumed metabolites. They
found that chloroacetic acid showed no mutagenic effects on
11
bacterial cultures, while vinyl chloride, chloroacetaldehyde, chloroethanol, and chloroethylene oxide showed definite mutagenic properties. Wachtmelster, et al. (29,30) have also reported similar results, but found no mutagenic activity with vinyl chloride
until the system was activated by the addition of liver extracts to the cultures.
C. PRESENT METHODS FOR DETERMINATION OF VINYL CHLORIDE LEVELS
IN THE WORKPLACE AND IN AMBIENT AIR
The nature of vinyl chloride pollution requires a different
approach for monitoring of the environment than do many other
pollutants. It Is necessary to have continuous monitors for ambient
air In the workplace to determine Immediately If a hazardous
level of the gas exists at any given time. Also, If the action
level of one-half ppm Is exceeded, It Is necessary to Implement
monitoring of the breathing zone of each Individual worker In the
area. Clearly, two different analytical procedures are required.
Until recently, It was necessary only to monitor the air In
the work environment. For this purpose, a wide variety of methods
have been proposed. Christie, t al. described the use of refri
gerant leak detector lamps to determine a variety of halocarbons, including vinyl chloride (31). A detection limit of 50 ppm Is claimed, but many other halocarbons interfered with the determina
tion. Grosberg (32) described a colorimetric reaction for vinyl
chloride utilizing the oxidizing action of KMn04 on the double
bond. After oxidation of the vinyl chloride adsorbed on tubes
12
of activated charcoal, chronotropic acid Is reacted with the
formaldehyde produced to give a color that may be quantitated using colorimetric procedures. Ethylene is listed as an lnterferent
and sensitivity Is poor. Leichnltz described the use of Draeger
tubes at vinyl chloride levels above 100 ppm (33). Konig (3*0 and Foris (33) described the use of Porapak porous polymer beadB for the chromatographic determination of halocarbons, including
vinyl chloride. Direct injection of air samples onto the chroma
tographic column was used by both researchers. Arnold, et al.
described the use of infrared chemllumlnescence for the determina
tion of chloroethylenes (36). No detection limits were given.
Golding (37), and Lavery and tfllks (38) reported the use of long
path Infrared spectroscopy for the determination of vinyl chloride in Industrial atmospheres. Confer described a method whereby vinyl chloride was decomposed by exposure to ultraviolet radiation
on sampling (39). The decomposition products were then trapped
in deionized water for measurement of conductivity. Detection
limits were given as less than one-tenth ppm, and interferences were not found to be a problem. Driscoll and Warneck (JjO) described
the use of a photoionization mass spectrometer for the determination
of a variety of inorganic and organic air pollutants. The detec
tion limit for vinyl chloride was found to be two ppm, and the
method was interference free.
All of the above methods were proposed prior to the adoption
of the present standards for vinyl chloride. Of all of the methods
13
proposed, only those based on direct Infrared analysis or gas
chromatography have sufficient sensitivity and selectivity for
consideration as standard methods under current regulations. Even when gas chromatography Is applied, In most cases some method of
sample concentration Is necessary for levels below one ppm.
It Is possible to use cold traps or solvent trapping for
vinyl chloride determinations, but adsorption on a solid adsorbent appears to be a better and more reliable method. The two most
commonly mentioned adsorbent media are activated charcoal (41-44)
and porous polymers (45-48). However, only Ives (48) was successful
in trapping vinyl chloride on porous polymer materials. He accomplished this by cooling the tubes to dry Ice temperatures.
On the other hand, Ahlstrom, et al. specifically warned that the
porous polymers, including Tenax G.C., Chromosorb 102, and Forapak
Q do not quantitatively adsorb vinyl chloride (44). It must be
noted that only operations at room temperature were considered
as being valid for the adsorption step.
The above methods generally are used to monitor ambient atmospheres within the work area. Adaptations of the charcoal
adsorption tube have become the accepted practice for continuously monitoring the exposure of individual workers to vinyl chloride.
The procedure recommended by NIOSH (49) calls for the collection of vinyl chloride on an approved lot of activated charcoal contained within a glass adsorption tube. Air Is drawn
through the tube at a constant rate from the breathing zone of the
14
worker by a battery-operated pump. The vinyl chloride Is then desorbed by carbon disulfide. An aliquot of this solution Is then Injected Into a gas chromatograph equipped with a flame Ionization detector. Materials necessary for this method of sampling may
be prepared according to the procedure described by Kupel, et al.
(41) or purchased from one of several suppliers, most notably
Mine Safety Appliance Company or S.K.C., Inc.
The NIOSH report specifically stated that the recommended
procedure Is still tentative and that substitution of any other
equivalent method would be permissible. One possible alternate
method has been marketed by Bendlx Corporation (50). Activated
charcoal is given a proprietary treatment before It is placed In
the sampling tubes. Air Is drawn through them as before, but the vinyl chloride adsorbed by the adsorbent is desorbed by heating the
tube to about 2^0°C. The desorbed vinyl chloride is flushed directly onto the analytical column for separation and measurement.
Instrumentation for this procedure is available commercially from Bendlx Corporation. Another alternate method has been proposed recently by Levine, et al. (5I). An alumlnized gas sampling bag is evacuated and attached to a pump similar to the others. Air from
the breathing zone of the worker is pumped at a constant rate into
the sampling bag during the entire work day. At the end of the day samples may be withdrawn from the bag and Injected into the
chromatograph by means of a gas sampling valve.
15
D. DEVELOPMENT OF THE PRESENT METHOD
All of Che present methods for sampling of vinyl chloride
In a personal monitoring system have one comnon denominator. They all require a battery-operated pump to collect the sample. The flow from this pump must be carefully regulated to a constant,
known value for periods as long as eight hours. This has in the past proven to be a rather difficult task. The pump is also
rather heavy, weighing several pounds, and is noisy and cumbersome.
The method of Levine (5I) is even more cumbersome, because it
requires that the worker also wear a backpack enclosing a container with a volume of eight liters. These methods all utilize a gas chromatographic finish, but avoid recommending a specific set of
chromatographic conditions. Trace contaminants within a work area will vary widely from plant to plant, and perhaps even within a
plant, such that designation of a single chromatographic column
capable of successful separation of vinyl chloride from all possible
interferents would be an impossible task.
Out of compassion for the workers In the vinyl industry who
have often been burdened with a bulky air bag and/or a heavy,
noisy pump as a part of their daily work attire, and in the belief that there had to be a better way, we undertook this research project. Others in this research group (52-5U) had developed proven methods for the determination of certain inorganic gases by
trapping in a suitable absorbing solution the gas which permeated
through a polymeric membrane. Still other workers (55,56) had
16
published findings on Che permeation of organic vapors through
similar membranes. In view of these results, the possibility of developing a personal monitoring device using the permeation
technique of Relszner and West (52) has been explored.
The easiest decision of this research program was the choice of the analytical technique to be used for quantitation of the
adsorbed vinyl chloride. Quantitative gas chromatography Is
generally acknowledged as the method of choice for the determina
tion of most volatile organic compounds. It Is both highly specific
and highly sensitive. In light of the findings of Boettner and
Dallos (57)» a chromatograph with a flame ionization detector was
selected. For vinyl chloride there Is little or no gain in
sensitivity to be had by using an electron capture detector.
Since the experiences of our research group had shown that
the dlmethylsillcone rubber membranes had the highest permeation
constants for most compounds, the use of these membranes was
investigated. The single backed membrane was found to be highly
satisfactory for our purposes.Previous experience had Indicated that by changing the
adsorbing solution In back of the membrane, the permeation device
could be made specific for a variety of compounds. However, the earlier work was done with solutions chosen to trap Inorganic species. Previous work with vinyl chloride (42-44, 49) had established that activated charcoal was probably the most desirable
adsorbent for it and other very volatile organic species.
17
Experimentation showed that the charcoal was Indeed effective as
an adsorbent for use with the permeation device.The best means for introduction of the sample into the
chromatograph for analysis has been the subject of considerable
study. The use of carbon disulfide as a solvent is currently the accepted standard method. It has the advantage of allowing
the injection of duplicate aliquots for any given sample. It also
has several disadvantages. The dilution of the sample on desorption
by carbon disulfide is at least ^00 fold, due to the injection of
only a small fraction of the adsorbed vinyl chloride. The high
vapor pressure of both carbon disulfide and vinyl chloride at room
temperature makes accurate injection of a constant aliquot a
serious source of error. Finally, carbon disulfide itself is quite
toxic and has a highly disagreeable odor. Thermal desorption has
the theoretical advantage of introducing the entire sample onto
the column at one time. It has the disadvantage of being a "one-shot" method. If any component of the equipment should fall
to perform properly during an analysis, the results of that parti
cular analysis are lost. Consideration was given to the fact
that the permeability of vinyl chloride through the silicone mem
brane was unknown at the outset of the research, and to the fact
that no adequate hood was available in which to perform the carbon
disulfide desorption procedure. These two considerations resulted
in the selection of the thermal desorption approach as the method
of sample introduction.
18
The preparation of both standard atmospheric levels of vinyl
chloride and calibration standards for the Instrument were done
using the permeation tube approach of O'Keeffe and Ortman (55).
The goal of this research was to produce a personal monitoring device that Is small, lightweight, and uses a passive method of sampling. The actual analytical finish will leave some leeway for
adaptation to specific needs, and will be compatible with most currently accepted procedures In use by Industry at the present
time.
CHAPTER II
EXPERIMENTAL
A. APPARATUS FOR EXPOSURE STUDIES1. Basic Design of Equipment for Vinyl Chloride Exposure.The apparatus used for the exposure of the permeation devices
developed In this study Is essentially that described by Relszner
(58). First, laboratory air Is cleaned and dried for the prepara
tion of standard vinyl chloride atmospheres. Then, a permeation
device of the previous design was used for determination of the
feasibility of the approach. Finally, a personal monitoring
device was designed, constructed, and calibrated for further testing
in the field.
2. Design and Preparation of Permeation Tubes.
The permeation tube Is a device developed by O'Keeffe and
Ortman (55) to provide primary standards for trace gas analyses.
It has been further studied by a variety of authors (59~&2)> permeation tube, Figure 1, consists of a cylinder of FEP Teflon (tetrafluorethylene, hexafluoropropylene copolymer) normally one-
fourth inch In diameter, filled with the liquified gas of interest,
and stoppered at both ends. Preparation of the tubes in our
laboratory was accomplished by first stoppering one end of the
tube with a plug made from TFE Teflon (polytetrafluoroethylene)
and cooling the tube by Immersion in liquid nitrogen. A disposable
capillary pipet was attached to a lecture bottle containing vinyl
20
FIGURE I
THE VINYL CHLORIDE PERMEATION TUBE
I t
— TFE TEFLON PLUG
|h^1
r-ir~!
I O
1 ^ 1\ZJT\ll~ -H
-IJT\
l_ ~ l
VINYL CHLORIDE
FEP TEFLON
S T U B EUT|
C~i
C H -n
TFE TEFLON PLUG
21
chloride under pressure, by means of a short length of Teflon tubing. The pipet was then used as a nozzle to direct the flow of liquid vinyl chloride from the lecture bottle into the Teflon permeation tube. When the tube was filled, it was removed from the liquid nitrogen bath, allowed to warm slightly, permitting
vinyl chloride vapors to drive out any air in the tube, and stoppered with another Teflon plug. The tubes were stored in a
freezer, enclosed In a bottle containing activated charcoal, until needed.
For studies at low levels, a low rate tube was prepared,
Figure 2, according to the method of Reiszner (62), which is
similar to that of O'Keeffe and Ortman (63). A glass bottle was
prepared by sealing one end of a length of 10 mn OD Pyrex glass
tubing and drawing the other end to a 5 mm OD neck. The tube was
then filled with liquid vinyl chloride as before and stoppered
with a short length of FEP Teflon tubing sealed by a TFE Teflon
plug. This had the effect of providing a very short active area
of tubing and consequently a lower rate of permeation of vinyl
chloride than was possible with the standard tubes. The permeation tubes prepared in this manner were also stored under refrigeration
until a short time before they were needed.
3. Calibration and Use of Permeation Tubes.Since the rate of permeation of a gas through FEP Teflon had
been previously found to be highly dependent on temperature, it
was necessary to maintain the permeation tubes at a precisely
22
FIGURE 2
PERMEATION TUBE FOR LON-LEVEL WORK
FEP TEFLON TUBE
TFE TEFLON PLUG
PYREX GLASS BOTTLE
VINYL CHLORIDE
23
controlled temperature for both calibration and use. For this
purpose a water bath arrangement was selected and was maintained at a constant 30.0CHp.05oC for the duration of this study.
Calibration of permeation tubes Is normally done by a gravimetric procedure described previously (60). Weighings were
made of each tube every few days for the first two weeks and then
at regular Intervals thereafter for the duration of the useful life
of the tube. Because the Teflon tubing used for the manufacture
of the permeation tubes is not perfectly uniform throughout, it
was necessary to standardize each tube Individually, No previous
record of permeation rates for vinyl chloride through FEP Teflon
was found, so it was assumed that the rate would be similar to
the rates reported for other gaseous hydrocarbons; that Is, between
10" 6 and 10“ 8 grams per centimeter per minute. The actual rate
observed was ^+1 x 10"7 grams per centimeter per minute for the
standard tubes. For the low level tubes, measurement of the
active length of the Teflon tube was not possible due to design.
Observed permeation rates were approximately 2 x 10" 8 grams per
minute.Table 1 shows typical permeation data obtained from a
standard permeation tube. The tube showed a constant permeation rate
over its entire six month useful lifetime. At the end of this
period the supply of vinyl chloride liquid within the tube was completely exhausted. It should be noted that despite some effort
to entrap a portion of the polymerization Inhibitor In the
TABLE ICALIBRATION DATA FOR A TYPICAL VINYL
CHLORIDE PERMEATION TUBE*Weight loss
nate Weight (Gm) (ug/mln
11-18-74 8.060711-25-74 8.0107 4.8712-20-74 7.8235 5.15
1-24-75 7.5582 5.27
2-18-75 7.5559 5.49
5-17-75 7.1567 5.20
4-21-75 6.8982 5.15
5-19-75 6.685O 5.19
6-16-75 6.4849 5.14
Lifetime Average 5.22
*Active Length of tube was 13*6 cm.
25
permeation tube, in most cases an apparent polymerization reaction
occured within the tube. A small amount of dirty white solid formed after a period of about four months, but did not cause an
observable change in the permeation rates, as long as there was free liquid vinyl chloride present. No discoloration or polymerization has been observed to date in the glass low-level permeation
tube.Permeation tubes for the possible lnterferents sulfur dioxide,
nitrogen dioxide, allyl chloride, chlorine, and ethylene dlchlorlde
were prepared and calibrated by the methods described above. All
proved satisfactory although ethylene dichloride and allyl chloride
suffered from extremely low permeation rates.
h. Preparation of Standard Vinyl Chloride Atmospheres.The preparation of various levels of vinyl chloride in air
required for these studies was accomplished by the apparatus
Illustrated by Figure 3 . Laboratory air was pumped by pump A
through a column of activated charcoal, B, for the removal of any
trace contaminants, and then through columns of silica gel, C,
for the removal of moisture. This clean, dry air then flowed through
valve D for regulation of the flow rate, which was monitored by
flowmeter, E.The regulated stream of air then passed through the mixing
chamber, F, which contained the vinyl chloride permeation tube, G.
This mixing chamber was kept in a constant temperature water
bath, H. The water bath, as mentioned previously, was maintained
FIGURE 3
APPARATUS FOR PREPARATION OF
VINYL CHLORIDE-AIR MIXTURES
LU Q
r
u -
u
y i O
o
o
m
CD
27
at a constant 30*00°C by a precision thermostat operating a
resistance heater. Finally the vinyl chloride->air mixture passed
into the exposure chamber, I, into which permeation devices were placed for study.
This equipment was essentially that used by Reiszner, et al.
(52- 5b). The only major modifications made were in the mixing
chamber and some of the interconnecting tubing. Because vinyl
chloride is highly soluble in polyvinyl chloride, the use of Tygontubing for connection of the mixing chamber and the exposure
chamber was not feasible. It was suggested (6b) that wherever
possible metal tubing be used, and everywhere else, either Teflon
or Nylon tubing be employed. In order to facilitate this a new
mixing chamber was developed, Figure b, using stainless steel tubingTMand modified Swagelok fittings. It allowed the direct connection
of the mixing chamber to the exposure chamber through copper tubing,
eliminating vinyl chloride losses by permeation through the tubing.
Also, unlike previous designs, it was leakproof under up to 25
pounds per square inch pressure.
5. Flowmeters.For all measurements of flow, rotameters were used. With
careful use they are capable of measuring air flow reproducibility
to + 2<jl> at full scale. Since the response of the rotameter was
dependent on pressure, every effort was made to minimize pressure
drop througout the system. To verify that pressure drop was not
a problem, checks of flow rate were made periodically at the exhaust
28
FIGURE k
MIXING CHAMBER FOR USE WITH
VINYL CHLORIDE PERMEATION TUBES
K*Vi
1/4" TEFLONTUBING
SWAGELOK FITTINGS
STAINLESS STEEL PLUG
MACHINED •TEFLON INSERT
1/8" COPPER UBING
I STAINLESS STEEL TUBING
14
29
of the system which vented to the atmosphere. Good agreement
was found at all but the highest flowrates employed, and a correction was made for these to Insure the validity of the measurements.
6. Permeation Device for Preliminary Studies.Since dimethylsllicone rubber membrane had been selected for
use, It was decided to use the permeation device developed byRelszner (52) for monitoring sulfur dioxide levels, (Figure 5).The device consisted of a glass tube covered on one end by a onemil thick silicone rubber membrane. The membrane was attached
to the tube by means of silicone rubber cement. The device then
was inserted into a one-hole rubber stopper to provide a seal
when the unit was Inserted into the port of the exposure chamber.
The adsorbent was placed inside the device and the open end wasTMcovered by a Saran film. The entire device now was ready for
insertion Into the exposure chamber for studies.
7. Additional Constant Temperature Baths.
For the purpose of conducting studies on the effect of
temperature changes on the permeation rate of vinyl chloride, it
was necessary to provide a number of constant temperature water baths. The bath described previously was adequate for studies at
30°C and a similar bath was set up and thermostatted at 1j0oC.
For studies at 0°C, a stirred ice water bath was set up.8. Standards for Instrumental Calibration.
As with any analytical procedure, it is necessary to properly
calibrate the method utilized for the determination. It is
FIGURE 5PERMEATION DEVICE USED FOR PRELIMINARY STUDIES
RUBBERSTOPPER
GLASS ^ TUBE
ADSORBER
MEMBRANE
31
particularly Important when using a gas chromatograph equipped with a flame ionization detector, since even a slight change in
any one of three separate gas flow rates can significantly alter the detector response. A good standard should be as similar to
the sample as possible. With this in mind it was decided to collect the vinyl chloride emitted by a permeation tube for a
measured period of time on the same lot of activated charcoal being
used for the actual analyses. This would eliminate some of the
problems that have been reported in the literature concerning
differences in the adsorption and desorption of organic compounds by different lots of activated charcoal. For this purpose, the
apparatus depicted in Figure 6 was constructed. It consisted of
a cylinder of nitrogen, A, to provide a flow over the vinyl
chloride permeation tube, B, contained in the mixing chamber, C.
The exhaust from this chamber then flowed to a three-way valve, D,
which enabled switching from the sample tube containing the
adsorber, E, to a second tube, F, containing an equivalent amount
of charcoal which served as a compensator for backpressure created
by the charcoal in the sample tube. This arrangement was found
to be necessary because of increased backpressure created by
mounting the sample tube on the valve. Since there was a considerable volume of gas in the mixing chamber, accurate collection of
standards for low levels of vinyl chloride, involving short collection times, would be impossible without this pressure compensation.
The standards collected in the manner described here were found to
32
FIGURE 6
EQUIPMENT FOR PREPARATION OF
VINYL CHLORIDE STANDARDS
Q Ui
I \
53
yield highly reproducible responses upon analysis using the
thermal desorption procedure.9. Humidity Studies.
It was confirmed experimentally that the presence of moisture
in the air flowing over the vinyl chloride permeation tubes caused
no detectible change In the permeation rates. Therefore, a gas washing bottle filled with distilled, deionized water was placed
in the exposure apparatus immediately prior to the mixing chamber.
Dry air at the same temperature as the permeation devices was
bubbled through this bottle and became saturated with water vapor.
The humidified air was then passed through the mixing chamber
where the vinyl chloride was added, and into the exposure chamber.
10. Interference Studies.Where possible, standard gas mixtures were produced from
permeation tubes by air dilution. It was necessary to Isolate the
permeation tubes used for this purpose from each other to prevent
contamination of the liquid within one tube by that within the other
through reverse permeation. This was accomplished by using separate
mixing chambers for the tubes and externally mixing the resultant
airstreams. This method was satisfactory for sulfur dioxide,
nitrogen dioxide, and chlorine. The less volatile organics required
a modified approach.For the accurate dispensing of less volatile compounds,
diffusion tubes, illustrated by Figure 7» were prepared. This was
done by sealing the large end of a disposable pipet and filling
3h
FIGURE T
DIFFUSION TUBE FOR VOLATILE LIQUIDS
CAPILLARY END
PYREX GLASS BOTTLE
LIQUID
35
the bottle so formed with the liquid of Interest. Calibration then was done by the same gravimetric techniques used for permeation tubes. The rate of diffusion from the tube was dependent on the length of the capillary which was adjusted, therefore, to provide the desired level of Interferent required within the limitations of the technique. This procedure was used for preparation of
allyl chloride and ethylene dlchlorlde-alr mixtures.
Finally, for the study of ozone, the ozone generator described
by Relszner (58) was used. Ozone was generated by exposure of
air to ultraviolet radiation within a twenty liter Pyrex bottle.
A mercury vapor germicidal lamp (GE-OZljSll) connected In series with a sixty watt light bulb produced the necessary ultraviolet
light. The concentration of ozone produced by this procedure was
determined by the standard colorimetric method and an appropriate
quantity of the ozone-alr mixture was then added to the vinyl
chloride-alr mixture for the study.
For all lnterferents studied, the air containing the possible
Interferent was mixed with the vinyl chlorlde-alr mixture Immediately prior to their entrance Into the exposure chamber. This
minimized the possibility of a chemical reaction between the species that would reduce the level of vinyl chloride prior to the exposure
of the permeation device.
11. Design of the Personal Monitoring Device.
The goal of this experimental work was to develop a permeation
method, and from the method so developed, design a simple personal
36
monitoring device. The principle design considerations were
small size, light weight, and convenient operation. The final design is illustrated by Figure 8. The body of the device was
manufactured of aluminum, taking advantage of its light weight and
easy machinability. The dimethylsilicone rubber membrane was cemented to the back portion of the device with silicone rubber
cement. The port for addition of the adsorber was closed with a
machined plug of TFE Teflon. The clip for attaching the device to
the clothing of the worker was taken from a discarded film badge.
The overall size of the device was h.2 by It.8 centimeters, and the overall weight was only thirty-five grams. This corresponded
closely to the size and weight of the film badge that had been in
use for the personal monitoring of radiation exposure for many years.
B. INSTRUMENTATION
1. Gas Chromatograph.
The gas chromatograph utilized for the analytical finish in
these studies was a modified Varlan Model 1200 with flame ionization
detector. Modifications were made in the flow system of the carrier gas to provide for a dual mode of sample introduction. These
changes, illustrated by Figure 9, permitted the use of either the thermal desorption or the carbon disulfide desorption technique with a minimum of effort to change from one method to the other.
A Whitey three-way valve, B, was installed on the downstream side
of the Nupro fine metering valve, A, used for flow control.
FIGURE 8
DESIGN OF A PERSONAL MONITORING DEVICE FOR VINYL CHLORIDE
BACK
4.2 CM
4.8 CM
0.6 CM
2-56 THREADED
1.5 MM
FRONT
4.5 MM
2.5 MM
1.5 MM
CLIP
TEFLONPLUG
!-56SCREW
j ■ < ■"■0
MEMBRANE
FIGURE 9
MODIFIED VARIAN 1200 GAS CHROMATOGRAPH
FOR VINYL CHLORIDE DETERMINATIONS
HELIUM CARRIER
F
nD
39
Position 1 then permitted the use of the instrument in its normal mode of operation, through the injection Port, C. Position 2 bypassed the injection port, shunting the flow of carrier gas through the thermal desorption unit, D, before sending it to the
column, E, through an added fitting.2. Column.
The chromatographic column selected for these studies was six feet of one-eigth inch stainless steel tubing, packed with
Chromosorb 102. This packing material had several advantages over other, more conventional column packings. Chromosorb 102 is one of
the new porous polymer packings. It exhibited low column bleeding
which makes for a low background and Increased sensitivity. It
also provided clean, rapid separation of low molecular weight
hydrocarbons, and caused only relatively small changes in flowrate
of the carrier gas and hence only small shifts in the baseline when
temperature programming was employed.
3. Recorder.A Honeywell-Brown Model Y11+3X Recorder was utilized in these
experiments. It had a range of -0.05 to +I.O5 millivolt full scale, and a chart speed of one-half inch per minute. The recorder was
equipped with a Disc Chart Integrator for accurate quantitation
of peak areas.
1+. Apparatus for Thermal Desorption.
The apparatus used for thermal desorption of vinyl chloride,
Figure 10, was designed and built within our laboratory. It
FIGURE 10
APPARATUS FOR THERMAL DESORPTION OF VINYL CHLORIDE
VARIAN 1200 GAS
CHROMATOGRAPH
1*1
consisted of a rotameter, A, for monitoring carrier gas flow rate,
a Whitey four-way valve, B, and a demountable sample holder, C, within a heated compartment, D. The four-way valve permitted the bypassing of the sample holder while it was being changed. Sample
holders were constructed from one-quarter inch thin wall stainless steel tubing, attached by means of Swagelok fittings. Heat for
desorption was provided by blowing the exhaust of a Master Appliance
Corp. Model HG501, I5OO watt heat gun through the thermally shielded housing containing the sample holder.
C. REAGENTS AND MATERIALS 1. Vinyl Chloride.
C. P. Grade, Matheson Gas Products, minimum purity 99*9$*2. Activated Charcoal.
Darco G-60, 20-40 mesh, from Matheson, Coleman, and Bell. The charcoal as shipped had a considerable amount of water adsorbed on
it. Before use it was treated by heating to 350°C. for 24 hours
under a flow of inert gas. This was necessary to remove not only the water but also any other adsorbed material that might interfere
with the analysis.
5. Chromosorb-102.
Johns, Manville Company, 60-80 mesh.
D. ANALYTICAL PROCEDURE
The determination of vinyl chloride involved two steps, namely,
collection of the sample and analysis. The sample was collected by
placing 1.0 gram of activated charcoal in the permeation device, and exposing the device to the vinyl chloride-air mixture. The charcoal was then removed from the device, and transferred to a
stoppered vial for storage. For the analytical step, the charcoal was transferred to a sample holder which was then mounted in the desorption oven. The carrier gas was allowed to flow through the
sample holder for five minutes, during which the charcoal was
rapidly heated to 00°C. to desorb the vinyl chloride. Hie desorbed
vinyl chloride was flushed from the sample holder onto the analytical column by the carrier gas. The analytical column was main
tained at ambient temperature during this phase of the analysis
to trap the vinyl chloride sample on the first few inches of its
length. After the vinyl chloride was desorbed and trapped on the
analytical column, the carrier gas flow was bypassed around the
sample holder. The column was heated to 95°C. for five minutes
until the vinyl chloride peak emerged, and then to 190°C. to flush
other compounds from the column. The column was then cooled to
room temperature in preparation for the next analysis.
CHAPTER III
RESULTS AND DISCUSSION
A. THEORY OF PERMEATION IN POLYMERS
The theoretical aspects of permeation of gases through
polymeric membranes have previously been well documented (58), so they will not be discussed in great detail here. Permeation of a gas through a polymeric membrane occurs as three distinct steps.
First, the gas is dissolved in the membrane material. Next the gas migrates through the material by a diffusion process. Finally,
the dissolved gas evaporates at the back side of the membrane.
These phenomena lead to the generalized equation, (l), describing
permeation.
(i) N - PA(Pl - pg)s
where N = flow rate of gas across the membrane,
P = permeability,A » area (cm2),s = thickness of the membrane,
and (px - p2) = difference in partial pressures across the membrane.
Permeation occurs because of the natural response of any system
to a stress applied to it, according to Le Chateller's Principle.
When the system is at equilibrium, px is equal to p2 and there is no net gas flow across the membrane, since the p1 - p2 term of Equation 1 Is zero. When an adsorber of the gas is placed on the
back side of the membrane, this equilibrium is disturbed, and gas flows through the membrane by the permeation process. The ideal adsorber is one that completely removes any gas that permeates
ithrough the membrane from the system. This drives p2 to zero and establishes the situation where the rate of permeation for a
given membrane is dependent only on the partial pressure of the
gas on the outside of the membrane. It should be noted that the
permeability term Includes all of the properties of the membrane-gas system; the solubility of the gas in the membrane, as well as the
diffusion coefficient of the gas through the membrane.
Since both solubility and diffusion coefficients are somewhat
temperature dependent, there is often a change of permeability found when the temperature changes* Relszner (52) found a slight negative change of permeability for sulfur dioxide as temperature
increased, while Bell (53) found a rather large positive change for for carbon monoxide.
Hie other factors influencing the rate of permeation are of
physical origin. An Increase in the area of the membrane exposed
to the gas will increase the amount of gas permeating for obvious reasons. An increase in the thickness of the membrane causes a decrease in the rate of permeation in accordance with diffusion theory
Because of the special methods that were required for the
production of membranes of the nature of those utilized in this
study, it was necessary to determine a permeation constant for each
device used. This constant was derived mathematically from Equation 1
Since the activated charcoal adsorber removed essentially all of
the vinyl chloride that penetrated the membrane, the value of p2 was very close to zero. Thus, Equation 1 became Equation 2.
(2) N = ?AP-—s
Multiplication of both sides of this equation by the time of exposure, t, gave the total amount of vinyl chloride, c, found on
the charcoal, expressed as:
/ \ PApxt(5) c - Nt - ------ .
Now, since px is simply a concentration term, some constant, a,
can be found that relates pi to parts-per-milllon of vinyl chloride,C. Equation 3 then becomes
PAaCt(h) a
where px » aC.
Now, it becomes possible to gather all of the constant terms into a single constant, k, for each permeation device.
Now, Equation 1| becomes:
f£\ Ct(6) c - T .
Equation 6 may be rearranged to give the final equation which allows the calculation of average vinyl chloride exposures from the
U6
chromatographic data, Equation 7.
(7) t *
and
where C “ average concentration of vinyl chloride (ppm),
c - amount of vinyl chloride found (ug),
k ■ an experimentally determined constant,
t = time of exposure.
B. DETERMINATION OF THE PERMEATION CONSTANT
Since the tabulated values for permeation constants did not
include the value for vinyl chloride, this value was experimentally
determined. Several permeation devices were exposed to a constant
level of vinyl chloride using the procedures described previously.
Analysis of the data so obtained allowed the calculation of the
permeability of vinyl chloride through silicone rubber membranes, and the permeation constant for each of the permeation devices.
is high, falling in the same range as that of saturated hydrocar
bons. This was encouraging information because it meant that the area of the membrane could be kept small while retaining a low
detection limit.
C. EXPERIMENTAL CONDITIONS FOR THE DETERMINATION OF VINYL CHLORIDE The primary purpose of this research was the development of a
monitoring method for industrial use. This required that the
The observed permeability of 800 x 10~9cm3 gas x thickness(cm)time(sec.)x area (cm2) x P(cm Hg)
analysis time be kept as short as possible. Current methods
required analysis times of approximately 25 minutes per sample, so this was chosen as the upper limit for this method. This became a significant consideration in the choice of the packing
material for the analytical column. Chromosorb 102 was selected because it produced the required separation and had a short retention time for vinyl chloride. The best combination of column
temperature and carrier gas flow rate was experimentally determined
to be 95°C with a helium flow of 30 ml per minute. This provided
a vinyl chloride retention time of approximately four minutes.
The conditions for thermal desorption of vinyl chloride have been
reported in the literature by several authors. (h3,hktcy0). Unfortuna
tely, their reports contained significant differences, so an experimental determination was made. Identical samples were prepared for
analysis. Desorption for a fixed time while varying temperature
was employed to determine the optimum temperature for desorption.
Then using this temperature, the time factor was varied. These studies showed that desorption was complete at temperatures above
270°C and at times longer than four minutes. As a result of these
studies, desorption for five minutes at 300°C, was adopted as the procedure for all subsequent determinations.
D. TEMPERATURE EFFECTPrevious studies had indicated a variety of temperature effects
that were observed for different compounds. Sulfur dioxide had a
u&
very small negative effect and carbon monoxide had a rather large
positive effect. To determine the effect of temperature on the permeation rate of vinyl chloride, exposures were made to a fixed
concentration of the gas at temperatures of 0, 23, 30, and 1j0oC. This covered the range of temperatures most likely to be found in facilities producing vinyl chloride or its related products. The
results of this study are presented in Figure 11. There appears
to be a very slight positive temperature effect. However, all
values found fell well within the range of experimental error for
the determination, making it impossible to state with certainty
that there Is an observable temperature effect.
E. RESPONSE OF THE SYSTEM TO VARIOUS VINYL CHLORIDE LEVELS
A major concern when this study was begun was the ability of
the activated charcoal to completely adsorb the vinyl chloride permeating through the membrane. All previous permeation studies
had Involved the chemical reaction of the species permeating through the membrane with an adsorbing solution, removing it irre
versibly from the system. For the study of vinyl chloride, a suitable reagent could not readily be found, and even if it were
found would probably be much less specific than gas chromatography.
Therefore, the use of activated charcoal was investigated, and proved satisfactory.
The concentration range studied in this work was to a large
degree determined by the experimental limits of the method used for
FIGURE II
EFFECT OF TEMPERATURE ON PERMEATION
OF VINYL CHLORIDE
TEMPERATURE
(°C)
JiG. VINYL CHLORIDE PER 8 HR EXPOSURE
0 ^ 0 o o o
o
o
roo
CMo
4*o
50
preparation of the standard vinyl chloride concentrations. Fortunately, the upper limit of 50 ppm corresponded with the previous Federal standard, and was an order of magnitude higher than the maximum level permitted under the current standards. It was not possible to accurately reproduce levels of vinyl chloride below
1 ppb using our methods. Also, at levels of 1 ppb, working condi
tions within the laboratory and instrumental considerations were
such that efforts to generate lower levels of vinyl chloride did
not seem to be worthwhile. It should be noted that 1 ppb is three
orders of magnitude lower than the current maximum permissible
level. The response of the system to vinyl chloride is illustrated in Figure 12. This response was linear over the entire range
studied. Also, even at the limit of 1 ppb, precision was within
the +50$ limit specified by NIOSH for an acceptable method of analysis.
Calibration of the instrument for these studies was accomplished
by adsorbing a known amount of vinyl chloride on an aliquot of
activated charcoal identical to that used within the permeation
devices. The amount of vinyl chloride adsorbed was within 10$ of the amount anticipated to be on the charcoal in the permeation
device after exposure. ThlB procedure was found to be necessary
due to the varying response of the detector to a given amount of
vinyl chloride, and the non-linearity of the detector response over
the wide range of sample sizes. Several standards were run during
the course of the analysis of a given set of samples as a check
FIGURE 12
RESPONSE OF THE PERMEATION DEVICE
TO VARIOUS VINYL CHLORIDE LEVELS
(AG.
VINY
L CH
LORI
DE
DETE
CTED
PE
R 8
HRS. IOOO —
100
1.0
0.1 -
0.01
2023LOG CONCENTRATION VINYL CHLORIDE (PPM)
52
on the detector response.
During the course of these studies, It was observed that the
geometry of the sample within the sample holder played an Important part In the accuracy of the results. When the sample holder was
used for the collection of the standard and then transferred directly to the thermal desorption unit, most of the vinyl chloride was on the charcoal In the extreme upper part of the tube, near the carrier gas Inlet. Subsequent analysis gave surprisingly low re
sults. When the transfer of the charcoal was accomplished by
Interconnection of the collection tube and the sample holder by a short piece of Teflon tubing, most of the vinyl chloride was adsorbed
on charcoal near the bottom of the holder. Vexy high results were
obtained In these cases. Finally, transfer of the charcoal to a
vial where It was mixed gave a uniform distribution of vinyl chloride throughout the sample holder, much like that found with charcoal from the permeation device. These results are presented In
Table II. Heating the samples for a longer period of time, up to 20 minutes, during thermal desorption did not have any observable
effect on the response of the Instrument. Treatment of the charcoal with hydrogen and heat to reduce any possible reactive sites
also had no effect on the desorption efficiency. This effect casts doubt on the results reported by any laboratory using calibration
by any absolute means such as a gas sampling system. It Is essential
to calibrate the Instrument by means of a procedure as much like
that used for analysis as possible.
53
TABLE II EFFECT OF GEOMETRY ON
VINYL CHLORIDE DESORPTION
Location within tube
TopUniform Bottom
Integrator counts observed
30too
1070
54
F. RESPONSE TIMEStudies were made to determine how rapidly the membrane
responded to changes of vinyl chloride exposure. As stated previously, permeation depends on three Independent processes. The
success of the endeavor depended on the rate at which the system
attained an equilibrium state between these three processes. For
thlB determination, a permeation device was exposed to a constant
level of vinyl chloride In the system. Every ten minutes, the
charcoal adsorber Inside was removed and replaced with fresh
adsorber. The length of time required to attain a constant rate of permeation through the membrane Is indicated by the amount of
vinyl chloride found on each fraction. Figure 13 illustrates the results of this study. No detectlble differences were observed for
any of the samples collected. This Indicated that the rate of permeation of vinyl chloride through the silicone rubber membrane
was very rapid. The estimated upper limit of the response time
was thirty seconds, but probably it was much lower than that.
G. HUMIDITY EFFECTAs in all previous studies, the preliminary work was done in
a system having a near zero relative humidity. For real analyses, particularly In the Gulf Coast area where the majority of the vinyl
chloride monomer used In this country is produced, this was an
artificial situation. Humidity was not expected to interfere with
the analysis, but to confirm this presumption studies were made
at a relative humidity of 100$. No detectable differences were
FIGURE I5RESPONSE TIME OF THE PERMEATION DEVICE
TO VINYL CHLORIDE
jG
VINY
L CH
LORI
DE
FOU
ND
5 -
20 30TIME (MINUTES)
56
observed between the response from these studies and those at zero
relative humidity for the same level of exposure.
H. INTERFERENCE STUDIESInterference studies were run on several common pollutants
that may be encountered In the vicinity of plants producing vinyl chloride. These Included sulfur dioxide, nitrogen dioxide, ozone,
ethylene dichlorlde, and chlorine. The results of these studies
are summarized in Table III. In every case except for that of
ethylene dichlorlde, the deviation observed between the experiment
using only vinyl chloride and that incorporating a possible inter-
ferent was within the experimental error of the technique. However,
for the case of ethylene dichlorlde, a large positive interference
was observed when the thermal desorption method was used for the
vinyl chloride determination. It was immediately confirmed by a
subsequent experiment, that pure ethylene dichlorlde produced a
large chromatographic peak corresponding to vinyl chloride when it
was thermally desorbed from charcoal. Further experimentation,
utilizing the carbon disulfide extraction procedure, resulted in
the elimination of the Interference by ethylene dichlorlde.
I. FIELD EVALUATIONThe field evaluation of this device was carried out with the aid
of a local industry. Six calibrated personal monitors, together with
a quantity of activated charcoal, were supplied to the Industrial
hyglenists at a local plant for evaluation and comparison to the
57
TABLE III
EFFECT OF COMMON INTERFERENTS ON VINYL CHLORIDE DETERMINATION
Interferent
NoneSulfur Dioxide
NitrogenDioxide
Ozone
ChlorlneEthyleneDichloride(l)
EthyleneDichloride(2)
InterferentConcentration
it. 5 ppm
5 PPm 2 ppm
57 ppm
5 PPm
5 PPm
tig. Vinyl Chloride Found
LO.itO
lO.itO
10.51+ 10.82 20.80
10.68
IO.96
PercentageDeviation
+1.30+if.O
+100
+2.7
+5.^
(1) Vinyl Chloride determined by thermal desorption.
(2) Vinyl Chloride determined by carbon disulfide extraction.
58
standard charcoal tube procedures. The calibration of the devices was carried out by exposing them to a one ppm concentration of
vinyl chloride for an eight hour period. Five duplicate determinations were made with each device. The permeation constants were
evaluated for each determination and the mean value was calculated for each device. The devices were then sent to the plant for study.
These personal monitors were worn concurrently with the sampling
pumps, equipped with charcoal tube adsorbers, by various employees within the plant. After exposure, the charcoal was removed from the devices and, together with that from the charcoal tubes, deter
mination of vinyl chloride was made by the carbon disulfide extrac
tion procedure. Twelve sets of data are available and are presented
in Table IV.The concentration range found in this study was from 0.02 to 8.9
ppm. Absolute deviation was determined by subtracting the value
found by the charcoal tube from that found by the permeation device.
Relative deviation was calculated by division of this deviation by the vinyl chloride concentration obtained by the charcoal tube method and was expressed as percentage deviation.
Examination of the data showed that the level of vinyl chloride
as determined by the permeation devices was in most cases between
20 and 50 per cent greater than that found using charcoal tubes.
However, it must be noted that the results obtained by the permeation
devices for the final six determinations contained duplicate values
for the devices. For these cases, two permeation monitors were worn.
59
TABLE IV
COMPARISON OF RESULTS OBTAINED WITH THE PERMEATION
METHOD TO THOSE USING PUMPS
PPM Vinyl Chloride Foundpermeation Charcoal Permeation Absolute Percentage
Sample Device Tube Device Deviation Deviation
1 1 6.9 8 .9 2 .0 29
2 2 0.83 0 .9 8 O.I5 18
5 3 0 .1 0 0.17 0.07 70
4 1 3.6 5.1 1.5 42
5 2 0 .05 0.16 0 .11 220
6 3 0 .1 0 0.15 0 .05 50
7 2 0.07 0 .1 2 O.O5 715 0 .1 1 0.04 57
8 3 0.07 0 .0 5 -0 .0 2 -29it 0 .0 8 0 .01 14
9 2 0 .50 0 .5I 0 .01 25 0.1t9 -0.01 -2
10 3 o.ltl 0 .it2 0 .01 2It 0.48 0 .0 7 17
li 2 0 .0 2 <P.05 _ _ _ _ m m
3 <0.05 • m
12 it 0 .8 8 O .92 0.04 55 0.97 0 .0 9 10
60
For all of these cases except the eighth determination, the
results obtained by the two devices were within 10 percent of each other. Even the eighth determination yielded results within the OSHA limit of 50 per cent deviation, though they represent a
data point near the detection limit of the method.
The high values found for the permeation monitors may be
rationalized by an inspection of the analytical procedures involved. The calibrations of the devices were made by using thermal desorp
tion for both standardization of the instrument, and determination
of the permeation constant. All charcoal used was from the same lot,
and was subjected to the same treatment and handling procedures.
The results of the field studies were obtained by using the carbon disulfide extraction procedure. The Instrument was standardized by
using a sample of vinyl chloride dissolved in carbon disulfide. This
standardization procedure assumed that the vinyl chloride is quanti
tatively extracted from the charcoal. Recent data indicated that
this was probably not a valid assumption. Also, the charcoal adsorption tubes were prepared from a different lot of charcoal which
may have had significantly different properties. Finally, studies by Cuddeback, et al. (65) have shown that the performance of charcoal tubes is not uniform even within a given lot. Breakthrough
of vinyl chloride occurred relatively rapidly at low levels, while
It was less rapid at higher levels, using the percentage lost as a
criterion for breakthrough. This effect can be amplified by local
conditions such as relative humidity or levels of other pollutants.
61
Despite these deviations from Ideal analytical procedures, the results of the field studies were most encouraging. No problems were encountered other than the relatively constant differences
in the comparison of the results. This could have been a serious problem, had the permeation monitor results been the lower of the
two sets of values, but it was almost a certainty that the devices were not creating any vinyl chloride. The most likely cause of
the deviation resulted from the different techniques employed by
the two laboratories.The new procedure was considered promising by the industry
involved. They are presently continuing their studies with the
goal of resolving the differences observed between the two methods.
CHAPTER IV
CONCLUSIONS
At the beginning of this work, several goals were set for
the final form of the personal monitoring device being developed.
Fortunately all of these were met or exceeded. The development and
characterization of a personal monitoring device for vinyl chloride
was a resounding success and was accomplished with a minimum of experimental problems.
This work describes a personal monitoring method that is far
more convenient than previous methods. The device employed is
very light in weight, and very small. It is completely portable,
requiring no external source of power. Production of the devices
can be readily accomplished at a minimal cost. Effects of tempera
ture, humidity, and conmon interferents on the results of vinyl
chloride determinations are negligible. The method Inherently does
the Integrated sampling that is required by OSHA. All criteria for an analytical method for vinyl chloride determination in personal
monitoring programs set forth by NIOSH have been met. The conven
ience of use is far superior to previous methods, and field studies
have indicated an enthusiastic acceptance of the method by workers
having previously used other methods.It may also be noted that the device described herein affects
only the method of sampling for vinyl chloride. Almost all
laboratories that are currently using adsorption of vinyl chloride
62
63
by charcoal In their personal monitoring program need not make
major alterations in their present procedures of analysis. For the samll operator, the charcoal adsorber may be removed from the
devices and sealed In glass vials for shipment to a central labora
tory for analysis. Studies indicate no significant losses from samples stored in such vials for periods up to six months.
Further extension of this work to vinyl chloride does not appear necessary at the present time. In the event of a drastic
reduction of allowable exposure, investigations Into methods for lowering the background may be necessary. Other possible areas for
future investigations are alternate methods for sample introduction,
and the development of other adsorbers having characteristics
superior to those presently available. Perhaps this may be
accomplished by coating the charcoal with a small amount of an
Inhibitor to polymerization, such as phenol or hydroquinone, or a
stationary liquid phase, as Bendix. Corporation has apparently done.
Also, the future development of a porous polymer similar to the
Porapaks and the Chromosorb Century series that exhibits better adsorption of low boiling gases at room temperature would be welcomed for study. Finally, there is still room for some design improve
ments of the sampling device to facilitate the addition and removal
of the adsorber.The personal monitoring device for vinyl chloride represents
the first application of this technique to trace analysis for organic
air pollutants. Further studies along these lines are clearly
6k
indicated. Studies are currently underway with NIOSH support on the hazards to health of a variety of other volatile organics
commonly found in the workplace. Among these, chloroform, vinyl- lidene chloride, and 1,1 ,1-trichloroethane are suspected health hazards, and probably can readily be detected by this method. Since
the strict regulation of one or more of these is likely in the
near future, they represent good candidates for further investiga
tions. Charcoal would probably prove to be an adequate adsorber
for the more volatile compounds, while the porous polymers such as Tenax G. C. are probably better for the remainder. Finally,
there Is a strong possibility that two separate devices could be
developed to handle the monitoring of exposure to most or all of the
organic vapors in the industrial environment, and some of the inorganic ones. One device would contain charcoal adsorber, and
the other a porous polymer. Two chromatographic analyses would
then give a complete record of a workers dally exposure to hazardous
vapors. Overall, the future of using permeation as a means for
sampling in the working environment appears to be bright.
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33* Leichnitz, K., 'Draeger Tubes for Vinyl Chloride11. Draeger- Hefte 2J1, 20-23 (1968).
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70
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VITA
Leonard Hoyt Nelms was born in Atlanta, Georgia on October 2 5, 191+6. He was educated in the Madison County, Georgia Public
School system, and was graduated from Madison County High School in I96U.
He attended the University of Georgia in Athins, Georgia and
was graduated with a B.S. in Chemistry degree in 1968. He entered
the University of North Carolina at Chapel Hill, North Carolina
and was graduated with an M.A. degree in Chemistry in 1972.
He married Josephine Whitney Nixon in March 1970* A daughter,
Jennifer Whitney, was born in November, 1972.
Mr. Nelms entered the Graduate School of Louisiana State
University, Baton Rouge, Louisiana, in June, 1972. While at the
University, he was elected to membership in the Phi Lambda Upsllon
Honorary Chemical Society. Mr. Nelms is presently a candidate for
the degree of Doctor of Philosophy at the University.
73
EXAMINATION AND THESIS REPORT
Candidate:
Major Field:
Title of Thesis:
Leonard Hoyt Nelms
Chemistry
The Development of a Personal Dosimeter for Vinyl Chloride Utilizing the Permeation Approach.
Approved:
C/\I.—Ia/jM aj«r Professor and Chairman
Dean of the Graduate School
E X A M IN IN G C O M M ITTEE:
I[I
Date of Examination:
April 22, 1976